The production of polymeric foams is well known in the art. For example, foams of amorphous polymers such as polystyrene have been manufactured for decades. Most commercial foam production processes involve the use of chemical blowing agents (CBAs) which decompose during processing or blowing gases like CFCs or carbon monoxide, which are toxic or polluting. Such foaming techniques generally produce foams whose cell sizes are on the order of millimeters and have mechanical properties much weaker than those of the solid form of the parent polymer material.
Structural foams have more recently been processed from polymers such as polymethacrylic imide and polyvinyl urea-amides. The production of such foams poses several problems. In the case of the former material, for example, the foam is manufactured by hot foaming methacrylic acid and methacrylonitrile monomers using carbon monoxide, a toxin, as the blowing agent. Additionally, such foams remain "macrocellular" and do not demonstrate mechanical properties anywhere near those of the parent polymer material.
To overcome the mechanical property deficiencies of macrocellular foams, the production of microcellular foams has been proposed. In these cases, microcellular foams were defined as having cell sizes on the order of tens of microns and cell densities on the order of 10.sup.8 -10.sup.9 /cc. Such a process was developed for the production of amorphous polymeric foams. This process involved saturation of the polymer sample with a non-reactive gas such as nitrogen at elevated pressure and a temperature below the T.sub.g (glass transition temperature) of the polymer. The pressure was then released and the temperature raised above the T.sub.g of the polymer. These techniques required soaking times on the order of 24 hours to allow the gas to dissolve in the polymer. These efforts to produce microcellular foams have been conducted primarily with amorphous polymers, although some more recent efforts have been made to use the process to foam semi-crystalline polymers such as PET.
High temperature polymers such as liquid crystalline polymers (LCPs) are more difficult to foam. In fact, to our knowledge, there are currently no LCP foams available because of the lack of a high temperature blowing agent as required by conventional "blowing" or foam manufacturing techniques.